Field of the Invention
The present invention relates to a copper alloy sputtering target.
Specifically, the present invention relates to a copper alloy sputtering target used as a target during sputtering when, for example, a copper alloy film serving as a wiring film such as a gate electrode, a source electrode, or a drain electrode in a thin film transistor is formed on a substrate made of glass, amorphous Si, silica, or the like through sputtering, and particularly to a sputtering target made of a Cu—Ca-based alloy (Ca-containing copper alloy).
Priority is claimed on Japanese Patent Application No. 2013-179386, filed on Aug. 30, 2013, and Japanese Patent Application No. 2014-149940, filed on Jul. 23, 2014 the content of which is incorporated herein by reference.
Description of Related Art
A flat panel display such as a liquid crystal display or an organic EL display has a structure in which a thin film transistor (hereinafter, expressed as “TFT”) and a display circuit are formed on a glass substrate or the like. Meanwhile, the recent requirement for a large size and high definition flat panel television creates a demand for a large size and high definition display panel in which the above-described type of TFT is used (TFT panel).
In the past, a wiring film made of an aluminum (Al)-based material was generally used as a wiring film such as a gate electrode, a source electrode, a drain electrode, or the like in a large-size high-definition TFT panel; however, recently, to decrease the resistance of the wiring film, the use of a wiring film made of a copper (Cu)-based material having a higher conductivity than Al is advancing.
A variety of copper alloys have been proposed as the copper-based material used for a wiring film for the above-described TFT panel. In recent years, a Cu—Ca alloy has drawn attention as described in, for example, Japanese Unexamined Patent Application, First Publication No. 2009-215613 and Japanese Unexamined Patent Application, First Publication No. 2011-044674. A wiring film made of a Cu—Ca alloy does not only have a lower specific resistance than an Al-based material but also has excellent adhesiveness to glass or the like that is a substrate material. Meanwhile, in a case in which a wiring film of a TFT panel is formed using the above-described type of Cu—Ca alloy, it is normal to apply sputtering, and in this case, a sputtering target made of a Cu—Ca alloy is used. The above-described type of sputtering target is manufactured through, for example, steps of casting and hot rolling.
Meanwhile, there is a case in which abnormal discharge occurs during sputtering. Here, the term abnormal discharge refers to a phenomenon in which, compared with a normal current flowing during normal sputtering, an extremely large current abruptly flows, all of a sudden, and an abnormally large discharge occurs. When the abnormal discharge occurs, there is a concern that the film thickness of a deposited film formed through sputtering, which serves as a cause of particle generation, may become uneven. Therefore, it is desired to avoid abnormal discharge during sputtering as much as possible.
Therefore, Japanese Unexamined Patent Application, First Publication No. 2013-014808 discloses a target in which the average grain diameter of Cu—Ca-based crystals is regulated in a range of 10 μm to 50 μm to suppress the occurrence of abnormal discharge during the sputtering of a sputtering target made of a Cu—Ca alloy.